Beer is mainly made of barley malt that serves as the source of starch and enzyme. The production process of beer is classified into a malting process, a brewing process, and a packaging process. In the malting process, malt is steeped into water for germination. During germination, degradative enzymes are activated. The germinating barley is called green malt. After germinating to an expected extent of modification, green malt is dried (kilned). In the next brewing process, water is added to ground malt and is heated for saccharification, and then, is filtered. The filtered liquid is boiled after adding hop, and saccharified liquid (wort) is obtained by separating hop dreg. After cooling, the wort is fermented by adding yeast, and is stored at a cold temperature. After carbon dioxide generated during the storage is dissolved into the fermented liquid (beer), and flavor is matured, the beer is filtered. In the packaging process, the beer is antiseptically filtered and is contained in barrels and/or bottles for distribution.
The quality of beer heavily depends on the quality control of the malting process, that is, the quality of produced malt. In general, a germinating process takes about four to six days. During germination, enzymes are synthesized, and starch and protein are partially degraded. The grade of malt degradation is referred to as “modification”.
In the production process of beer, it is important to control the malt quality. Kohlbach Index, Hartong index at 45° C., diastatic power, viscosity, and β-glucan content are indexes that indicate the quality of malt. These parameters are controlled in the malting process to maintain constant malt quality.
The parameters for indicating malt modification are described below.
Kohlbach Index: the ratio of the nitrogen amount of congress wort prepared for analysis and the nitrogen amount of the whole malt. It indicates the extent of protein degradation in the malt. The higher the Kohlbach Index is, the more the malt is degraded. (modified).
Hartong index at 45° C.: the ratio of the extract of 45° C., 1-hour mashing of fine ground malt and the extract of the congress wort. The amount of extract mainly depends on the amount of starch and sugar. In malt, the degradation of protein components existing among starch particles affects the amount of extract. Accordingly, Hartong index at 45° C. indicates the degradation grade of both starch and protein. The higher the Hartong index at 45° C. is, the more the malt is modified.
Diastatic power: To determine the starch degradative enzyme power of malt, the amount of reduced sugar generated by affecting water-extraction liquid of malt to soluble starch is measured using iodometry. The starch degradative enzymes are synthesized as the barley germinates. In a brewing process, these enzymes are required for degradation of starch in malt and in adjuncts (for example corn starch). Malt with low diastatic power may cause a problem in a beer brewing process.
β-glucan content: β-glucan is the degradative product of cell wall of the malt. If the cell wall is not degraded enough, the lautering of mash becomes not smooth. Beer with high β-glucan content may cause haze after freezing.
The β-glucan content is measured as follows: after ground malt is heated in ethanol to inactivate enzyme, β-glucan in the malt is degraded to glucose by processing with lichenaze and β-glucosidase; and the amount of generated glucose is determined using glucoseoxidase/paroxidase method.
Viscosity: the viscosity of congress wort prepared for the analysis. Polysaccharides such as starch, dextrin, β-glucan, and pentosan mainly affect the viscosity of wort. The viscosity indicates the degree of degradation of stored starch and cell wall. The lower is the viscosity, the more the malt is moderated. The viscosity is measured at 20.00° C. with Ubbelohde type viscometer.
Friability: Friability is measured by a dedicated friability meter. Specifically, the friability is measured as follows. After being ground with a roller, malt samples are separated into one that passes through a specific slit and one that does not pass through the specific slit and remains. The separated malt samples are measured. The friability of the malt samples is defined as the ratio between the separated malt samples. Malt of which starch and cell wall are not well degraded is crystalline and consequently hard. Friability of such malt is low. Well degraded malt is mealy and easy to grind. The friability of such malt is high.
Conventionally, the above parameters for analyzing the modification of malt are determined with general analytical methods such as chemical analysis. However, the general analytical methods have problems such that the preparation and measurement of samples require considerable time. A rapid and simple analytical technique for malt quality evaluation is needed.
There are many analytical techniques for analyzing material, such as chemical analysis, optical analysis, and physical analysis (using X-ray, for example). Recently, electron spin resonance (ESR) analysis is drawing attention as an analytical technique to obtain molecular level information of material. The application of ESR analysis is being intensively studied.
The principle of ESR is exactly the same as that of nuclear magnetic resonance (NMR). ESR is a kind of magnetic resonance spectrum. Whereas the NMR measures the resonant absorption of nuclear spins, the ESR measures the resonant absorption of electron spins. The ESR most directly reveals information about the molecular structures and electron states of materials having unpaired electrons such as a radical and a transition metal complex (trivalent iron ion and bivalent copper ion, for example). As of now, the ESR is the most reliable analytical technique for detecting radicals.
ESR spectra show the following: g value indicating the position of resonance of the unpaired electrons, resonance intensity indicating the number of unpaired electrons, absorption width related to relaxation time, and hyper fine structure caused by the coupling between the unpaired electrons and atoms (1H and 14N, for example) having nuclear spin near the unpaired electrons. Since each of radical species exhibits an intrinsic position of absorption, one can identify the radical species based on the g value. Additionally, one can consider reaction time and reaction mechanism based on the change over time of absorption (intensity).
The inventors intensely studied the application of ESR to the evaluation of state (quality) of malt in beer brewing. As a result of the study, the inventors discovered that, if an absorption intensity (signal intensity) is observed, the radical species is roughly identifiable based on the g value, and that there is a correlation between the absorption intensity (signal intensity) and the state (quality) of green malt and malt. The present invention, which is made based on the above discovery, provides a more rapid and simpler method of evaluating the quality of malt, than that of conventional analytical techniques.